Here's a really handy little tool to keep on hand if you have
one of the great older Whirlpool-built dryers. It's made for both 29" (wide) and
27" models.

Hang this card inside the drum (instructions are included) and run the dryer for
15 seconds or so. If you open the door and the card has fallen off, airflow
through your vent system is OK. If the card's still hanging, it's time to get to
work cleaning the vent ducting - and probably the inside of the dryer, too.

Poor airflow, usually from lint buildup, is the #1 cause of
problems with dryers, and is responsible for more dryer-related fires than any
other cause.

This is one of the items I no longer stock, but they're still
available on Ebay from my distributors,
HERE
(I've shortened the LONG Ebay URL to make it easier to deal with)

"Nothing astonishes men so much as common sense and plain
dealing" - Ralph Waldo Emerson